A 13.56 MHz band RFID (Radio Frequency IDentification) system or NFC (Near Field Communication) system is a technology that performs non-contact short-distance wireless communication between (i) an IC card or an IC tag and (ii) a reader/writer. Such an IC card or IC tag is provided with an IC chip and an antenna coil, and an antenna coil is also provided in the reader/writer.
By making the IC card or the like close to the reader/writer, magnetic flux is generated by electromagnetic induction that is generated between these antenna coils. As the magnetic flux is exchanged between the IC card or the like and the reader/writer, power can be supplied, and information that has been written to the IC chip can be exchanged.
At that time, if metal such as a communication circuit or the like is integrally arranged at a rear surface or the like of an antenna coil within a casing, an eddy current is generated in the metal due to the generated magnetic flux, and this eddy current generates a magnetic field in a direction opposite to the generated magnetic flux. As a result, there will be problems such that the generated magnetic flux weakens, and a communication distance shortens, or communication cannot be performed. Additionally, thermal loss is also generated due to the generation of the eddy current.
To solve such problems, arrangement of a magnetic body is proposed, which is constituted by a material with high magnetic permeability between an antenna coil and metal. In general, magnetic permeability μ is expressed as complex magnetic permeability μ=μ′−jμ″ (j is an imaginary unit). A real part μ′ of complex magnetic permeability is a material constant showing a normal complex magnetic permeability component, and an imaginary part μ″ is a material constant showing a loss. These material constants become factors that control a communication distance in short-distance wireless communication. In order to improve the communication distance, it is important to concentrate the magnetic flux by a high μ′ while suppressing thermal loss by a low μ″.
NiZn ferrite material has high resistivity, so a loss in a high-frequency band can be suppressed. NiZn ferrite material is often used as a magnetic body material for a high frequency. In particular, by including CoO, various techniques are implemented so as to improve a high-frequency characteristic. For example, in Patent Reference 1, a characteristic as a magnetic core member for an antenna module is improved by including CoO. Additionally, Patent Reference 2 discloses addition of cobalt ferrite (CoFe2O4) that is spinellized in advance so as to improve dispersiveness of Co. In Patent Reference 3, a selective reaction of CoO is controlled by adding Co2O3. However, such a high-frequency material is accompanied by deterioration of the real part μ′ of complex magnetic permeability, and if such a material is mounted as an antenna element, there was a problem that a sufficient communication distance could not be obtained.